(1) Field of the Invention
The present invention relates to a gas sensor, particularly for a current-type gas sensor.
(2) Description of the Prior Art
Basically, current popular conventional gas sensors according to the operation mechanism can be categorized into following types: catalytic combustion type, oxide semiconductor type, solid state electrolyte type (using sensing electric voltage, current or resistance as signal), field-effect transistor type (FET), infrared type and so on. By electrode configuration of the conventional technology, the popular conventional gas sensors can further be classified into electrode coplanar configuration and electrode un-coplanar configuration. In the early phases, the conventional gas sensors of electrode un-coplanar configuration take the dominance, which are further sorted into tubular profile, planar profile and compound profile. Whereas, the conventional gas sensors of electrode coplanar configuration are apt to be adopted in popular manner because the thin-film technology is gradually improved and advanced. Moreover, the gas sensors can be grouped into electric voltage signal kind and electric current signal kind in accordance with the sensing method and detecting signal. Nowadays, a combinational gas sensor in merging the electric voltage signal kind and electric current signal kind emerges from the automobile industry.
FIG. 1 is an illustrative schematic view for a conventional current-type oxygen sensor 10. As shown in the figure, the oxygen sensor 10 comprises a first catalyst electrode 11, a second catalyst electrode 12, an electrolyte layer 13, a gas diffusion cavity 14 with a gas diffusion opening 17, a power supply 15 and a galvanometer or current meter 16. The power supply 15, which is usually a battery, is electrically connected to both of the first catalyst electrode 11 and the second catalyst electrode 12. The current meter 16 is parallel connected to the power supply 15. The first catalyst electrode 11 is located in the gas diffusion cavity 14. The gas diffusion opening 17 is bored at the top surface of the gas diffusion cavity 14.
Upon performing detecting operation, the power supply 15 will provide a voltage to both of the first catalyst electrode 11 and second catalyst electrode 12 to initiate of the gas sensor 10 so the oxygen gas is enabled to enter into the gas diffusion cavity 14 via the gas diffusion opening 17. In the gas diffusion cavity 14, the oxygen gas is chemically is ionized into oxygen ion by the first catalyst electrode 11 so a limiting current is generated by the flow of gas ions and/or electrons from the first catalyst electrode 11 to the second catalyst electrode 12 by the oxygen vacancies in the electrolyte layer 13. Thereby, by measuring the magnitude of the limiting current via the current meter 16, the ambient oxygen concentration can be determined. Normally, the measured limiting current signal value of the current meter 16 is direct proportional to the partial oxygen pressure in the ambient atmosphere.
Regarding the conventional current-type gas sensor, the thickness of the electrolyte layer 13 will affect the sensitivity of the gas sensor 10, which means the thinner for the thickness of the electrolyte layer 13, the better for the sensitivity of the gas sensor 10 is. However, subjecting to the material feature of the electrolyte layer 13, the thickness reducing of the electrolyte layer 13 has its critical limit otherwise it is susceptible to break if it exceeds its critical limit. Moreover, the conventional current-type gas sensor requires operating in higher working temperature for keeping stability because the conductor material of able ionization adopted by the conventional electrolyte layer 13 is almost solid electrolyte. Accordingly, an extra conventional heating accessory is needed to maintain the higher working temperature. However, if sudden fluctuation happens in the ambient temperature, the conventional heating accessory is usually unable to adequately response in adjustment for the suitably corresponding working temperature with result that the detecting accuracy of the conventional current-type gas sensor is harmfully affected.